Electric arc apparatus



ept19,1944. H. w. BCIDUSMAN ETA..." 2,358,620

ELECTRIC ARC APPARATUS ori inal Filed Jan. 18. 1938 Gases to separating tower m4" l/guid hydro carbon sum;

Inventor's:

Henry W Bousman,

John B. Miles, rt,

Their Attorne'zg.

2,358,620 anaemic rsns'rus H W. usman, ficotia, N. it, John B.- Mlles, (in, Greenville, Deb, assignors, by direct and mesnc assignments, to General Electric Company, a corporation of New York application Jm I? s, r 1

18, 1938, Serial No.

185,d98. Divided and application February 1d, 19M, Serial No. 378,886

4 Claims. (c1. 204-327) This invention relates broadly to the operation of an electric arc and, more particularly, to

means of maintaining an are between a plurality of electrodes situated or immersed in a medium of high dielectric strength such, for example, as liquid hydrocarbon. The present application is a division of our application Serial No. 185,498, filed January 18, 1938.

The invention is especially concerned with certain improvements and modifications in means for striking and maintaining an electric are such as described for instance in United States Patent No. 1,930,964, issued October 18, 1933 to Joseph Bethenod.

Inaccordance with the Bethenod patent an electric arc is struck and maintained between two electrodes immersed in a liquid hydrocarbon by means of pilot sparks formed by a succession of high frequency discharges. The frequency of succession of these discharges is described as being of the order of magnitude of a musical frequency. Apparatus for carrying the Bethenod process into effect comprises a main source of alternating current connected to electrodes, which also are connected to an auxiliary circuit comprking a condenser; and, in addition thereto, an alternating-current generator, having a materially higher frequency than that of the main source of alternating current, for charging the condenser. A spark gap is provided which is rotated synchronously with said alternator and is arranged to discharge the condenser across said electrodes. Such apparatus has been used, for example, for producing from liquid hydrocarbon a raw gas comprising mainly acetylene and hydrogen, from which gas the acetylene subsequently may be separated. The yield of l ns and of acetylene therefrom per unit of time heretofore has not been satisfactory. Power consumption per unit volume or weight of gas prodnced also has been excessive.

It is a principal object of the present invention to provide an improved apparatus for operatlng an electric arc in a medium of high dielectric strength. for instance, in a liquid hydrocarbon.

Another object of the invention is to material- Bethenod invention. so as to permit substantial increase in the voltage of an arc between electrodes in a medium to be reacted and thereby to obtain an increased yield of reaction products per unit of time.

Another object of the invention is to obtain an increased yield of gas, especially an increased yield of acetylene, from a unit of liquid hydrocarbon, than obtainable by the apparatus described in the preceding paragraph and in Bethencd Patent No. 1,930,964, with lesser power consump! tlon per unit of gas produced by the apparatus.

Other and further objects of the invention will be apparent to those skilled in the art as a reading of this specification proceeds.

In accordance with the present invention the tween a condenser of an auxiliary or so-called' "pilot spark circuit and an electrode of the min are of the apparatus described and illustrated in the aforesaid Bethenod patent. v

The novel features which are characteristic of our invention are set forth in th appended claims. 'The invention itself, however, will be understood most readily from the following description when-considered in connection with th accompanying drawing in which the single figure isa diagrammatic view which illustrates by way of example one embodiment of the invention.

Referring to the drawing: Immersed in a, medium 1 of high dielectric stre gth, for example liquid hydrocarbon, such, for example, as gas oil contained in a suitable metal reservoir orare chamber 2, are electrodes 3 and d, which are'supplled with direct or alternating electrical current. Additional electrodes may be provided as desired, or as condian altemating-current generator or alternator E 1y prolong the duration of individual discharges of an auxiliary circuit comprising a condenser such as used, for example, in practicing the of low or industrial frequency and of suitable generated voltage. These electrodes may be tubular in form, consisting, for example. or carbon tubes with. thick walls, in which formthey may serve both as electrodes between which an arc is struck and maintained and as means for conductor 1 which is grounded at 8.

introducing liquid hydrocarbon into arc chamber 2. Carbon electrodes of this general type are described, for example, in Soulary Patent No. 1,964,832. In the drawing the liquid hydrocarbon is indicated by an arrow as being introduced into the arc chamber through the electrode 4, but of course it will be understood that either or both of the electrodes, when in tubular form, thus may be employed.

The arcchamber 2 is provided with an outlet 6 through which vapors or gases formed as a result of decomposition of the liquid hydrocarbon by the heat of the are are conducted to a suitable separating tower (not shown). Liquid condensate from the tower may be mixed with fresh charging stock and returned through the electrode 4 to the arc chamber 2.

The gases from the separating tower may be used as such, if desired,,or they may be separated further into their components, or a desired component, for example acetylene, may be freed of impurities with which it may be contaminated.

The electrode 4 is grounded to the arc chamher 2, the supply circuit being completed by the A pilot high frequency alternator 8, having a musical or audible frequency of, for example, 500 to 1000 pcriods per second, considtutes'an auxiliary generator which supplies current to the primary conductor of a transformer III. In practicing the present invention a pilot high frequency alternator 9 with a frequency of 1000 periods per second advantageously may be used in combinaation with a relatively greater powered low frequency alternator -.with a frequency of 60 periods per second.

The secondary leads of the transformer I0 are connected to one of the terminals of a condenser II and to the body of a metal box or case l2, which forms a screen for a. spark gap. This spark gap is shown by way of illustration as a rotary spark gap, the rotor I3 of which operates or rotates synchronously with that of the pilot alternator 9. Known means (not shown) are provided suitably to regulate the angular position at which a spark passes to the teeth of the rotor I3 with respectto the poles of the rotor'of the alternator 9.

The metal box I2 is connected with the conductor I and with the ground at 8. The electrode I4 also is grounded, while the insulated electrode I5 is connected to one pole of the transformer II), which pole also is connected to one of the terminals of the condensergl I. The other terminal of the condenser II is connected by means of conductor I6 to the electrode 3. An impedance shown by way of example as an inductance coil I1 is electrically interposed in the conductor I 6 between the condenser I I and'the electrode 3. The coil I1 is adapted to increase the duration of the individual discharges of the condenser II to a period permitting a substantial increase in the length of the arc path between the electrodes 3 and 4 without increasing the voltage available from alternator 5. Such increase in the length of arc path is accompanied by an increased arc voltage and an increased yield of gaseous reaction product. The conductor I6 and the inductance coil I] may be surrounded as. shown by a metal tube or shield I8 which constitutes the connection between the metal box I2 and the grounding cable 1. Such shield over said conductor and coil may be trically interposed in the conductor I9 and pro-- tects the alternator 5 against the passage of high frequency discharge currents. The condenser 20, which is connected to the terminals of the alternator 5, and an ohmic resistance 22' in series with a spark gap 23, constitute a convenient means for ensuring that the alternator 5. will not be subjected to dangerously excessive voltages. A

fan or blower 24 driven by any suitable means may be connected, as desired or as may be required, to the metal box I2, and serves to renew the atmosphere within said box. The vitiated air: passes outwardly to the atmosphere throug the opening 25 in box I2.

In operation, the periodic discharge through the gap between the electrodes 3- and 4 is ensured by the passage of the teeth of the rotor I3 in front of the electrodes I4 and I5. Each passage determines two sparks jumping simultaneously between each of these electrodes and the corresponding tooth of the rotor I3, thus producing a periodical short circuiting of the secondary of the transformer I0. At each short circuit, the voltage of the terminals of the condenser II is suddenly transferred between the electrodes 3 and 4, between which it is discharged if the voltage is sufficiently high. The number of discharges per second of the condenser II depends upon the number of teeth of the rotor I3 and generally will be either equal to or double the frequency of the alternator 9.' By arranging the rotor I3 in the metal box [2 and by surrounding the conductor IS with a metal tube I8 in the manner shown in the drawing, electromagnetic radiations are suppressed, and interference with radio communication is thus avoided. As an additional precautionary measure to obviate interference with radio receivers, the high tension terminal supporting the electrode 3 may be surrounded, if desired, by a metal hood.

We have found that the duration of the individual discharges of the condenser II, when the gaps between the teeth of the rotor I3 and the electrodes I4 and I5 break down, is determined by the capacity of this condenser and the distributed capacity and inductance of the leads (for example, 16, 12, 3, etc.) to the arc gap formed between the electrodes 3 and 4. have further found that the voltage from the alternator S that is obtainable across the electrodes 4. In an oscillatory circuit such as herein described, there will be additional half waves of electric current alternating in direction and of successively smaller magnitude. The duration of each of these half waves is one-half the reciprocal of the calculated resonant frequency of the" discharge circuit; that is, it is the approximate time required for one discharge of the condenser from zero current to zero current through one-.

half cycle. If the duration of an individual oondenser discharge that is oscillatory is increased, there is a decrease in the natural frequency of the high frequency discharge circuit; that is, a decrease in the rate at which the condenser in such circuit discharges. For purpose of brevity, current durations as above described are referred to herein as duration of individual condenser discharges."

By increasing the duration of the individual discharges of the condenser ii in the manner hereinbefore described, we are able to maintain the -main arc across a substantially widergap with a larger arc voltage and to increase substantially the yield of gas produced in a given time, with given electrical energy (kilowatt-hour) consumption. In other words, by practicing the present invention there is obtained an increased yield of gas per unit of electrical energy used per unit of time in a process of producing gas by subjecting a liquid hydrocarbon to the action of an electric are. For example, with 150 amperes current in a 60 cycle circuit from the alternator '5 and with a duration of individual condenser discharges of 1 micro-second, the quantity of raw gas produced per hourwas of the order of 500 cubic feet. By-increasing the duration of. individual condenser discharges to, for example, 7.2 micro-seconds, by means of an.inductancecoil placed in the circuit between the condenser II and the electrode 3, approximately 1500 cubic feet per hour of raw gas were produced.

The development of the discharge in a device of this kind takes place in the following order. Initially, electrons originating at the cathode traverse the spaceto the anode under the influence of the high gradients imposed by the inter-electrode voltage. These high velocity electrons make very few collisions with the gas molecules so that in general they may lose their energy only by ionization. In the case of the spark discharge which has a duration of microseconds, the process described above is complete in that period of time.

In the case of a persistent discharge, the subsequent development proceeds along the following lines. The energy which the electrons take from the field is transmitted to the electrodes, and to the gas molecules by processes involving the ab-- sorption of radiation. As the number of the ionizing collisions per unit of time increases, the electron energies decrease and the gas energy and temperature are raised, leading to a thermal equilibrium between all components of the discharge. The establishment of this equilibrium is synonymous with the formation of an arc discharge characterized by low potential gradient and high conductivity in the arc column. It is at this point that suflicient conductivity develops to allow power current to flow in the arc. The time required to develop this steady state high conductivity arc is of the order of 100 micro-seconds for the case in hand, which involves a train of half waves for each oscillatory discharge. The thermal equilibrium results from the cumulative effect of successive half waves of the oscillatory discharge. The flow of power current thus depends upon the development of this thermal equilihrium which is characterized by temperatures of the order of 6000 K., high electron density and high electric conductivity.

In the table are presented data taken while operating apparatus such as described in the aforesaid Bethenod patent, with and without an inductance coil in the auxiliary circuit.

Table Without With inductance inductance coil in the coil in the a cry auxiliary V .clrcuit circuit Open circuit volts l, 300' l, 270 Power-to motor oi main generator, kw 62 146 Power actor Low 0. 7-0. Power to motor of pilot spark, kw... 7 5 Cycles, power supply 60 60 Are gap, mm 1 4 to 5 Oil circulation, gallons per min 30 60 Temperature oioil, deg. C 35to99 $0 Yiel of raw gas in cubic feet per houn. 460 1. 600 Per cent by volume of acetylene in raw gas 33 30 Yield 0! acetylene in pounds per hour 10 34. 5 Kwh. per pound of acetylene produced. I 6. 9 4. 4

It is to be noted that by using an inductance coil in the auxiliary circuit of the apparatus, the yields of raw gas and of acetylene are more than tripled, with approximately two-thirds of the power consumption per pound of acetylene produced. In other words, by the practice of our invention the efficiency of gas production per unit of power is materially increased as compared with operation of apparatus having no inductance coil in the auxiliary circuit.

In practicing our invention we adjust the duration of individual discharges of the condenser ii in such manner as to permit greater separation of the electrodes 3 and d "for a given terminal voltage. The optimum condenser discharge rate may depend, for example, upon the composition, shape and area of the electrodes 3 and 4, upon the composition and dimensions of the arc chamber generally, and upon other variations in mechanical and electrical elements of the apparatus. In no case, however, is the duration of individual condenser discharges increased to the point at which a substantial portion of the energy stored in the condenser passes around the inductance coil 2|, the condenser 20 and through the conductor 7 to the ground at 8, since such action would decrease the effectiveness oi the condenser discharge in igniting the are at the 60 cycle current zero.

In practicing the present invention a polyphase are between more than two electrodes may be employed. However, for purpose of illustrating how this invention may be carried into effect, a system employing only two electrodes has been shown and described.

The invention may be carried out in various other modes of procedure than that herein specifically described. The scope of the invention is not limited to the medium in which the arc is maintained or to the purpose for which it is employed. For example, the medium may be water and the arc may be used to weld articles immersed therein, or the medium may be a compressed gas, for example air, hydrogen, nitrogen, methane, ethane or the like, under such high pressure, above atmospheric pressure that an arc therein otherwise would become unstable.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An apparatus for operating an electric are between electrodes situated in a liquid of high dielectric strength which comprises a primary circuit including a main source of cyclically varying electrical current connected to said electrodes, an auxiliary circuit connected in parallel charging said condenser across the said electrodes, to initiate discharges between said electrodes during the cyclic variations of said main source, said auxiliary circuit including an impedance device connected in series with said condenser whereby the duration of the individual discharges of said condenser is increased.

2. An apparatus for maintaining an electric are between electrodes situated in a liquid of high dielectric strength which comprises a primary circuit including a main source of alternating current connected to said electrodes, an auxiliary circuit connected in parallel with said primary circuit to said electrodes and comprising a condenser, an auxiliary alternator for charging the said condenser, a discharge circuitincluding a spark gap device which is operable in synchronism with said auxiliary alternator and which is connected to discharge said condenser across the said electrodes, and an inductance coil in said auxiliary circuit for increasing the duration of the individual discharges of said condenser.

3. An apparatus for generating gas by operating an electric are between electrodes situated in a liquid hydrocarbon which comprises a primary circuit including a main source of alternating current connected to said electrodes, an auxiliary circuit connected in parallel with said primary circuit to said electrodes and comprising a condenser and an auxiliary source of alternating current having a materially higher frequency than the said main source of electrical current er'across the gap between said electrodes, and an inductancev element in the discharge circuit of said condenser, said element having a suiliclently high inductive value to materially increase the efliciency of gas production.

4. An apparatus for generating gas by an electric are between electrodes situated in a liquid hydrocarbon, which comprises a primary circuit including a main source of alternating current of low frequency connected to said electrodes, an auxiliary circuit connected in parallel with said primary circuit to said electrodes and comprising a. condenser and an auxiliary alternator of an audible frequency which is connected to charge the said condenser, a discharge circuit including a synchronous spark gap for discharging the said condenser 'across the said electrodes, and an inductance coil connected in the discharge circuit between said condenser and said electrodes, said inductance coil having suilicient inductive value to cause the individual discharges of the said condenser to persist during a period of sufl'icient length to cause the energy consumption and the gas generation by said electric arc to be more than twice as high than would be the case in the absence of said inductance coil.

HENRY W. BOUSMAN. JOHN B. MILES, JR. 

